Aaron Alexis, the gunman who killed 12 people at the DC Navy Yard, had been stewing over a perceived slight for about a year, would stay up all night playing military-style video games, and kept asking friends for financial help, acquaintances of the shooter told ABC News.

One woman said she believes Alexis ruined her new car in a fit of anger when she couldn't give him rides.

The FBI is now scrambling to learn anything and everything they can about the shooter's past, which include previous brushes with the law and frustration about his pay as a consultant during a contracting trip to Japan and difficulties finding full time work.

Alexis, 34, began running into trouble as a Naval reservist in 2010. ABC News has found that the Navy sought to give him a general discharge, a status that is less than an honorable discharge. But the Navy was not successful and Alexis instead sought an honorable discharge through what is called the early enlisted transition program. He was honorably discharged in January 2011.

Alexis worked for Hewlett-Packard as an IT subcontractor for the Navy, the company said. He was an employee of a company called "The Experts" that refreshed equipment used on the Navy Marine Corps Intranet network. It was unclear if he was working at the Navy Yard itself where the shooting occurred Monday.

Alexis also volunteered as a waiter at the Happy Bowl Thai restaurant in White Settlement, Texas, until May 2013. Kristi Suthamtewakul, whose husband owns the restaurant, said Alexis lived with her family for a time. Suthamtewakul said Alexis became frustrated with his employment when he returned from Japan last year.

"For instance, he started talking about he was getting slighted with his benefits, they weren't paying him on time," Suthamtewakul told ABC News today.

Suthamtewakul said Alexis displayed more frustration when she wasn't physically able to give him rides to interviews or buy groceries.

"At the time my health was poor and I couldn't give him rides to do that and he just started getting frustrated with me like I owed it to him to give him rides," she said. "Then he started taking my food here and there, food that I had paid for. He continued to do little things like that."

Suthamtewakul said Alexis' behavior reached a tipping point when she suspected him of damaging her new car.

"We had parked our brand new Honda Accord in our garage and he's the only one that has access to it. And we have a fenced-in backyard and that's even got a lock on it. And he was at the house all day and apparently the next day it wasn't working. And Honda said someone had put sugar in the gas tank and there was only one person by deduction," she said.

Sources tell ABC News that Alexis, 34, recently bought a shotgun used in the attack at a Lorton, Va., gun store and that he may have gotten other weapons, including an assault rifle at the scene. As of now, there is no evidence of terrorism and the FBI believes he acted alone when he opened fired Monday.

Michael Ritrovato was a friend of the suspect and said he met him at an event at a Buddhist temple four years ago. Alexis, according to Ritrovato, was an avid fan of military-style video games and would stay up all night to play.

"He played all the time. That was his passion," Ritrovato told ABC News. "It got so bad – was in his room all the time… he'd be late for work. He just didn't want to get up early. The reason was because he was staying up all night playing video games."

"When he got that contract job, he said they did him wrong at first. They didn't pay him," Ritrovato added. "He called me and asked for a loan to help get his car fixed. I had my daughter's car in the shop, so I couldn't help him."

Alexis joined the Navy as a reservist from 2007 to 2011 and got his rank in 2009. He was an aviation electrician and he was detached from service for a series of misconduct issues, a Navy official said. The suspect had a security clearance that allowed him onto the Navy Yard as part of his civilian subcontracting work, officials said.

Alexis was arrested Sept. 4, 2010, by Fort Worth police after he was accused of recklessly discharging a firearm inside the limits of a municipality, according to the Tarrant County District Attorney's Office.

Alexis was previously arrested on May 6, 2004, in Seattle for shooting out the tires of another man's vehicle in what he later described as "an anger-fueled 'blackout,'" according to the Seattle Police Department.

He told cops he could not remember firing his gun at the man's car until an hour after the incident.

A Seattle detective spoke to Alexis' father, who was "curious" about the incident.

"Mr. Alexis then told me that his son had experienced anger management problems that the family believed was associated with PTSD," the detective wrote in a police report. "He confirmed that his son was an active participant in rescue attempts of Sept. 11, 2001."

Suthamtewakul said 9/11 had a profound impact on Alexis' life because he was living in New York City at the time of the attacks on the World Trade Center.

"He was living in New York, being from New York and he talked about how angry he was with the terrorists who would take innocent lives," she said.

Melinda Downs said she has known Alexis for about a year and despite always having a smile on his face he spoke about depression.

"You never saw him without a smile on his face or saying something to make a person laugh and when you would see him looking down I would just ask, 'Aaron, are you okay?' and he would be like, 'I'm okay. I'm okay.' And I would just keep talking to him until he would lighten up," Downs told Good Morning America today.

Downs spoke to Alexis as recently as last week and said he was in Washington D.C.

"He called checking in as usual," she said. "He was just his old chipper self."